Because of the toxicity of mercury, there is great concern over any discharge of mercury into the environment. Until relatively recently, chemical plants did not take the necessary precautions when disposing of materials containing mercury. As a result, the soils and waters surrounding these plants are often contaminated with mercury or mercury compounds. The process of cleaning soils contaminated with metals is difficult since metals are strongly absorbed or even diffused inside the pores of the soil matrix. Additionally, metallic mercury and most mercury species are not soluble in water.
If mercury exists in the soils in the presence of other metals, the removal process is even more costly and complicated. The price of disposing contaminated soils has increased dramatically in the past few years, particularly for disposal of mercury-contaminated soils, due to local, state and federal environmental regulations which restrict such disposal. Today, agencies that administer sites will usually require that the contaminated soils be treated rather than disposed of. In most cases, more than one process technology is required to clean up the soils to meet federal and local standards, especially if more than one metal is present in the soils. This makes the clean up of the site more difficult, time consuming and expensive.
Several methods have been developed to recover the mercury from the solid materials. U.S. Pat. Nos. 5,314,527, 5,013,358 and 3,755,110 disclose processes that remove mercury from muds, sludge or other materials containing mercury compounds. However, most of these methods are complex and/or inefficient. Some even resulted in the discharge of a dangerous mercury vapor into the environment.
It is therefore the object of this invention to provide a safe and efficient process for cleaning mercury-contaminated soils.
Another object of this invention is to provide an easy, economical and efficient process that can be used to clean soils contaminated with additional metals, such as zinc, copper and lead.